1. Field of the Invention
The present invention generally relates to a transformer, and more particularly, to transformer configured with an inner wiring inside a wiring substrate.
2. Description of Related Art
In a balance/unbalance filter, mutual inductance can be obtained by mutual coupling magnetic field between two inductors of a transformer, for single end transmission of differential signals. According to the trend of developing miniaturized electronic products, many electronic components have been integrated into a wiring substrate, such as passive components including capacitors, inductors, and resistors.
FIG. 1 illustrates a layout of a conventional transformer. Referring to FIG. 1, a conventional transformer 100 includes two plane coils 110 and 120, substantially positioned at a same plane. Each of the two plane coils 110 and 120 includes a plurality of loops. The loops of the two plane coils 110 and 120 are sequentially arranged one's across another's. With a specific circuit design, mutual inductance between these two plane coils 110 and 120 can be adjusted by adjusting sizes of these two coils. However, such an adjustment also varies self-inductances of the two plane coils 110 and 120. Therefore, the transformer layout employing such a design lacks design flexibility.
FIG. 2 illustrates a layout of another conventional transformer. Referring to FIG. 2, a conventional transformer 200 includes two plane coils 210 and 220, substantially positioned in a same plane and adjacent to one another. The transformer 200 is capable of adjusting mutual inductance between these two plane coils 210 and 220 by adjusting a distance between the two parties. However, even though the change of the distance between the two parties does not vary self-inductances of thereof, this design requires a larger layout area of the transformer 200.